DIY Audio Projects Forum

Vacuum Tube Rectifiers
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Author:  Gio [ 11 Jan 2011, 13:15 ]
Post subject:  Re: Vacuum Tube Rectifiers

Thanks for sharing this great info. I've book marked the thread and will definitely refer back to it in the future.

Author:  Les [ 11 Jan 2011, 14:16 ]
Post subject:  Re: Vacuum Tube Rectifiers

Wow, Matt. That 5U4 is a saggy tube. I hadn't ever looked at the 5U4. I've looked at the 6CA4 and the 5AR4. I've a build on the back burner that will be using the 6CA4. I looked at the 5AR4 for that build, but I like the small size of the 6CA4 and its current handling is sufficient for my build. If I were needing something with a little more umph, I would consider the 5AR4. But after looking at the 5U4, I can't under stand any use for that one unless you just needed some real current hog of an amplifier. To over come that sag, you would need a pretty high voltage PT supplying it.

Good thread Matt. Definitely gets the brain juices flowing. :thumbsup:

Author:  nkdk [ 17 Jan 2011, 08:30 ]
Post subject:  Re: Vacuum Tube Rectifiers

Dos anyone know the the Shuguang 274B rectifier tube,and are thy enny good,planning to use them in a single ended, b+ voltage abut 450-500 volts


Author:  rock4016 [ 18 Jan 2011, 11:06 ]
Post subject:  Re: Vacuum Tube Rectifiers

Here's a data sheet I found.

Should be similar to the Shuguang.

Author:  Suncalc [ 24 Feb 2011, 13:01 ]
Post subject:  Re: Vacuum Tube Rectifiers

It's been a while but I was looking over a power supply design and I began to think about the rectifier voltage drop plot out of Herbert Reich's 1944 book "Theory and Applications of Electron Tubes", 2nd ed. shown here in this thread. I had originally thought that the straight lines were just approximations but then I wasn't so sure. So I went back to my plot of voltage drops vs peak plate current and changed the axes types from linear to log. These two plots show the result.
lin-lin Plot.png
log-log Plot.png

The first is just the plot of numbers taken directly off curves in the data sheets. The second is the same plot with the axes changed.

Now I am wondering if there is anything to be learned about how these tubes operate from these relationships. And why are the slopes of all the lines on the log-log plot nearly identical. This must correspond to some fundamental characteristic of the tubes but I'm not sure what. Is this behavior a consequence of Child's Law? Do the tubes lower on the plot represent those with cathode materials having lower electron affinity? Does anyone have any ideas here. I'm curious.

Author:  bda [ 24 Feb 2011, 14:08 ]
Post subject:  Re: Vacuum Tube Rectifiers

With mention of Chinese 274 rectifiers : don't bother ! You'll get better sonics from a USA 5Z3 which is a 5U4G on a UX4 base . Cheaper and no doubt more reliable too . Try a paralleled pair of 5Z3 and you may thank me later...

I'm a big fan of DH rectifiers such as 5Z3 CV31 U19 and type 83 :)


Author:  rock4016 [ 24 Feb 2011, 20:08 ]
Post subject:  Re: Vacuum Tube Rectifiers

Probably not a good idea to use the 83 since It's a MV type and has the usual hazards associated with those type of tubes. Also I've heard Chinese 274B that did sound good, but NOS 5U4GB did sound better in the mono-blocks I heard them in.

Author:  Geek [ 24 Feb 2011, 22:05 ]
Post subject:  Re: Vacuum Tube Rectifiers

rock4016 wrote:
Chinese 274B that did sound good, but NOS 5U4GB did sound better in the mono-blocks I heard them in.

My 2A3 clients have said similar.


Author:  bda [ 25 Feb 2011, 03:46 ]
Post subject:  Re: Vacuum Tube Rectifiers

rock4016 wrote:
Probably not a good idea to use the 83 since It's a MV type and has the usual hazards associated with those type of tubes.

It's hearsay . I'm at a loss to find any reason why these devices are hazardous . Mercury is poisonous but is contained within the envelope . Yes there are caveats such as adding plate suppressor chokes and using an AM radio or search coil (a choke) to 'sniff' for RFI , if there is any , can be useful

MV's look good . MV's sound good...

What more can you ask for ?


Author:  rock4016 [ 25 Feb 2011, 10:17 ]
Post subject:  Re: Vacuum Tube Rectifiers

If the following is hearsay then please disregard my previous statement.

1) MV rectifiers that are new or have been laid on their side for some reason need to have their filaments run for 20-30 minutes without HV applied to make sure that the mercury is vaporized and out of the filament and other tube electrodes where it can cause internal shorts.

2) Under voltage on the filament (like only 10%) can cause immediate tube failure because of inadequate mercury vaporisation.

3) All MV rectifiers need to have their filaments warmed up for 45-60 seconds before HV is applied to assure that the mercury is vaporized. Failure to ensure adequate warm up time can cause back bombardment of the filament and destroy the oxide coating in a matter of minutes. This means you will need a separate filament supply with a switch or time-delay relay.

4) Mercury vapor rectifiers are prone to "arc-over" or "flash-over" caused by under or over vaporization problems and just random weirdness. If you have never seen an MV rectifier flash over just wait, if you are using them, and eventually it will happen. Tube implosions are very rare (caused by disentegrating and flying pieces of tube elements) but that was one of the reasons MV rectifiers were frequently in cages. Most big transmitters always had a spare rectifier that could be switched in when one of the MV tubes arced-over. It will scare the pants off you when it happens.

5) MV rectifiers, because of the gas plasma, can generate huge amounts of broadband noise that need to be filtered out by special "hash chokes" in the anode leads and by invasive bypassing. This doesn't always happen but it does occur frequently. This was another reason that they were in shielded cages.

6) MV rectifiers are temperature sensitive and need to be operated over a realtively narrow range.

7) Don't drop one! When one inadvertently gets broken, there is sufficient elemental mercury in a cold tube to constitute a significant environmental and hence health hazard. Clean up depending on the surface it spills on can be problematic, in any event it is usually recommended that a local hazzmat specialist do the clean up. There are recommended clean up procedures for fluorescent lamps which generally contain a lot less mercury afaik.

The worst case scenario might be if an operating tube got broken and the vapor escaped because it will quickly condense leaving micro-droplets of mercury on everything it touches.

I know an 83 is a long way from an 870B but it still is subject to the same problems on a smaller scale

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